72 4. A clean sample of 0.033 gram of magnesium ribbon is introduced in a eudiom

Question

72 4. A clean sample of 0.033 gram of magnesium ribbon is introduced in a eudiometer. The magnesium reacts with the H2SO4 solution in the eudiometer. The volume of the hydrogengas colected at 757 mmHg and 25.0°C is 35.10 mL. Determine the value of the gas constant R Mg 24.3 g/mol. MgH.SOMgSO4 + H2 5. A group of students perform an experiment to determine the value of the gas constant. They forgot to include the vapor pressure of water in their calculations. Will the value of the experimentally determined gas constant be high, low, or unaffected?

Explanation / Answer

Question 4

Balanced equation:
2 Mg + H2SO4 ===> Mg2SO4 + H2
Reaction type: single replacement

Mass of Magnesium = 0.033 gm

Moles of Magnesium = 0.033 gm /24.3 gm/mol = 0.001357

Moles of H2 produced =  0.0006788 moles

using the moles we can calculate the gas constant

PV= nRT

P = Pressure in atm                       V= Volume in Liter

n = no of moles               R = Gas constant in L atm K-1 Mol-1

T = Temperature in Kelvin

P = 757 mmHg = 0.99605 atm

V = 35.10 ml = 0.0351 Liter

n =   0.0006788 moles

T = 25 Deg cel = 298 K

Calculate Gas constant

R = 0.99605 x 0.0351 / 0.006788 x 298 = 0.01728 L atm K-1 Mol-1

Calculatre Gas constant value is 0.01728 L atm K-1 Mol-1

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